Anionic Palladium(0) and Palladium(II) Ate Complexes

Palladium ate complexes are frequently invoked as important intermediates in Heck and cross-coupling reactions, but so far have largely eluded characterization at the molecular level. Here, we use electrospray-ionization mass spectrometry, electrical conductivity measurements, and NMR spectroscopy to show that the electron-poor catalyst [L3Pd] (L=tris[3,5-bis(trifluoromethyl)phenyl]phosphine) readily reacts with Br- ions to afford the anionic, zero-valent ate complex [L3PdBr](-). In contrast, more-electron-rich Pd catalysts display lower tendencies toward the formation of ate complexes. Combining [L3Pd] with LiI and an aryl iodide substrate (ArI) results in the observation of the Pd-II ate complex [L2Pd(Ar)I-2](-).